In a conventional screw propeller for underwater thrust, a blade is tilted with respect to a main shaft at the part close to the center of the propeller and the blade twists from the center to the periphery.
JP8-72794A discloses a high-speed thrust machine in which a blade tilts rearward.
In a conventional screw propeller for ships, an angle with respect to oncoming fluid flow is large at parts close to the center of the propeller, so that the propeller is thick and water flow twists with rotation of the propeller.
When rotational speed increases, water flow does not circulate along the angle with respect to oncoming fluid flow. Fluid leaves the blade surface to produce cavitation to cause noises and bubbles.
Twisting of water flow and cavitation cause loss in rotational energy.